1. We instinctively still vote for the better looking candidate in elections and assume less guilt of the beautiful.
2. Instinctive tribalism to want to live around people like us, hence the most segregated time of day is when everyone is at religious worship and once there are enough people to achieve the density, ethnic enclaves form for immigrants
3. Every religion and political group says we're number one, those who disagree are at best ignorant and at worse evil, stupid, bad. John Cleese has a great Monte Python sketch on that Sargon of Akkad uploaded recently.